I've had my 2007 FEH for almost 3 years now - just barely still in warranty. Yesterday was a cold day (25 degrees F) and after the engine was fully warmed up, I switched the heater control to defrost while I was at a stop light. I was amazed that the engine didn't kick in, as I swear that it always has in the past. Has anyone seen this before and does it indicate a problem that I should have fixed while still under warranty?

I realize that the AC compressor clutch has a cold temperature lockout.

 

It probably depends on just what temperature the engine coolant happened to be at the time. And A/C being disabled at the time would DEFINITELY make a difference, no pre-COOLED airflow needing to be reheated before routing to the windshield.

Oh, what temperature were you requiring for the cabin...?? If the ICE wasn't needed, being used, at the time to heat the cabin then IMMHO SOP.

In yesteryear the system heat "setting" would have been automatically raised in defrost/demist/defog mode, but no more.

 

I thought that the ICE always ran at idle when the selector was in any of the orange marked positions (AC MAX, defrost, mix)

I was asking for heat and was in the floor position - just moved selector to the defrost position, while still in the heat mode

I'm not following you here.

 

Tom, the A/C compressor normally runs in the defrost mode and that's what requires the engine to run. In freezing weather damage to the compressor would occur if it runs so the compressor shuts down and no longer needs the engine to run. This is the only exception when you can go EV in the defrost mode if all other EV requirements are met. It's all normal.

GaryG

 

Gary-
I thought they went to electric compressors in 2010 models? That wouldn't need the engine to run.

 

That's true for the 2010 FEH and FFH but Tom has a '07 FEH. The electric A/C would also shut Off in freezing weather but EV is not effected by that A/C system. When I drove the 2010 BMW X6 ActiveHybrid I found that EV was hard to go into with the electric A/C running because the battery SoC kept falling below EV requirements in city driving. So both systems (engine belt driven and electric A/C) have their problems. I'm sure we could figure out a way to maintain the SoC level for EV in city driving and still get killer mileage with an electric A/C running. I just didn't have enough driving time in the X6 to hypermile with the A/C On.

GaryG

 

Why would running the compressor in freezing temperatures damage anything? Every vehicle I've ever had, assuming it was so equipped, ran the A/C compressor when defrost was on. For what it's worth, I have never at any temperature observed the ICE not to run with defrost on. Mine's an '06

 

"..Why would.."

Because that was the wrong answer.

The main reason A/C systems are shut down with OAT near/at/below freezing is to prevent the A/C evaporator from freezing up. If the OAT is already at or below freezing there is no productive work, not even dehumidification, the A/C cooling could do.

But.

It is also true that if operation were FORCED somehow then it would be highly likely that liquid refrigerant would reach the compressor inlet (the term is "slugging") and then damage would be done.

 

"..not following you.."

Before automotive A/C became so commonplace the way the system operated in defrost/defog/demist mode was to HEAT the airflow to the interior surface of the windshield. Even after A/C became more common it was used in conjunction with HEATED airflow.

Nowadays the idiot design engineers (mostly NipponDenso and/or Denso US) seem to not realize that the efficiency of the A/C is totally dependent on climatic conditions, whims of mother nature, so we're left, randomly, with non-functional defog/demist capability.

I just disassembled the climate control module in my Lexus LS400 so I could modify it to switch to fully heated, MAX HEAT, airflow when the defrost(/defog/demist) function is activated.

 

Here we go again Willard...

"To avoid compressor failure during cold temperature conditions, A/C systems use some type of electrical safety switch that must be operating properly to prevent compressor engagement. Switches performing this function include an ambient temperature switch that prevents compressor operation below 40 degrees Fahrenheit, a low-side pressure cycling switch that prevents compressor operation usually below 25 degrees Fahrenheit or an evaporator temperature switch that cycles the compressor off when the evaporator becomes cold."
http://www.asashop.org/autoinc/march2003/mech.htm

I also suggest those doing radiator blocks go to this link above for A/C concerns.

GaryG